Heat treatment unit, cooling unit and cooling treatment method

ABSTRACT

A substrate cooling unit comprises a cooling plate on which the substrate is placed, a cooling temperature adjusting element which adjusts the cooling plate to a predetermined temperature, a temperature controller which controls a temperature of the cooling temperature adjusting element according to a transfer function, a temperature sensor attached to the cooling plate, and a control parameter changing section which changes at least any one setting of a proportional operation coefficient, integral time or derivative time among control parameters in the transfer function based on a temperature of the cooling plate detected by the temperature sensor after the substrate that is an object to be cooled is placed on the cooling plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 11-328795, filed Nov. 18,1999, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a thermal treatment method of heatingor cooling a substrate such as, for example, an LCD substrate or asemiconductor wafer or the like, and a thermal treatment unit.

In processes of manufacturing semiconductor devices, thephotolithography is performed on a surface of a substrate such as, forexample, a semiconductor wafer (described as “a wafer” hereinafter) orthe like. In the photolithography, a sequence of processes are performedin which a predetermined pattern is exposed on the wafer after a resistsolution is applied on the surface thereof and subsequently developingis performed thereon.

In such coating and developing processes, heat treatment is performed onthe wafer if necessary after the resist coating, the exposing and thedeveloping, and thereafter cooling processing is subsequently performedto cool the wafer in a state of a high temperature, to a certain degree.

A heat treatment unit for performing heat treatment has a heating platein which a heater is embedded. The wafer is placed on the heating plateand subjected to heat treatment by heat from the heating plate. Atemperature sensor is attached to the heating plate so that atemperature of the heating plate can be monitored. A signal from thetemperature sensor is inputted to a controller for controlling atemperature of the heater based on the sensor signal sent from thesensor.

A cooling unit for performing cooling treatment has a cooling plate inwhich a Peltier element is embedded. The wafer at a high temperatureafter the heat treatment is placed on the cooling plate and subjected tocooling treatment by cold energy of the cooling plate. A temperaturesensor is attached to also the cooling plate so that a controllercontrols a temperature of the Peltier element based on a signal from thetemperature sensor similarly to the above-described heating plate.

Now, a state of the temperature of the heating plate when the wafer isheated up to a predetermined temperature is shown in FIG. 22. In a graphin FIG. 22, a horizontal axis indicates heating time [sec.] and avertical axis indicates the temperature of the heating plate [° C.].When the wafer is placed on the heating plate, the heating plate losesan amount of heat to the wafer and its temperature is lowered, as shownby Graph Line “k” in FIG. 22 (time t₁ to t₂ in FIG. 22). The controller,which recognizes the drop in temperature by the temperature sensor,increases an amount of electric power to the heater to start heattreatment. At this time, the temperature of the heating plate overshootssince heating by the heater is abruptly performed (time t₂ to t₃ in FIG.22). Subsequently, the controller, which recognizes the overshoot by thetemperature sensor, decreases the amount of electric power to the heaterto lower the temperature of the heating plate (time t₃ to t₄ in FIG.22). After passing through the processes as described above, thetemperature of the heating plate becomes stable. Incidentally, PIDcontrol, in which a proportional element, an integral element, and aderivative element are added, is adopted for the controller so thatexcess properties can be improved by reducing a deviation to a minimum.

Next, a state of a change in temperature of the cooling plate when thewafer after the heat treatment is cooled to, for example, 23° C. isshown in FIG. 23. In a graph in FIG. 23, a horizontal axis indicatescooling time [sec.] and a vertical axis indicates the temperature of thecooling plate [° C.]. As shown by Graph Line “1” in FIG. 23, thetemperature of the cooling plate maintains 23° C. before the wafer isplaced thereon. Then, when the wafer at a high temperature is placed onthe cooling plate, the cooling plate receives an amount of heat from thewafer and the temperature of the cooling plate is raised (time t₁ to t₂in FIG. 23). The controller, which recognizes the rise in temperature bythe temperature sensor, subsequently increases an amount of electricpower to the Peltier element to start cooling treatment. At this time,the temperature of the cooling plate undershoots 23° C. since cooling bythe Peltier element is abruptly performed (time t₂ to t₃ in FIG. 23).Thereafter, the controller, which recognizes the undershoot by thetemperature sensor, decreases the amount of electric power supplied tothe Peltier element to raise the temperature of the cooling plate (timet₃ to t₄ in FIG. 23). After passing through the processes as describedabove, the temperature of the cooling plate is stabilized to maintain23° C. Also in this case, PID control is adopted for the controller sothat excess properties can be improved.

Incidentally, the wafer having a temperature of, for example, 23° C. (aroom temperature) undergoes heat treatment at 200° C. in so-calledprebaking (PREBAKE) for the sake of heating-removal of a resist solventin a resist after resist coating, the wafer having a temperature of 23°C. undergoes heat treatment at 90° C. in post-exposure baking (PEB), andthe wafer having a temperature of 23° C. undergoes heat treatment at 30°C. in postbaking (POSTBAKE) performed after developing treatment.

Conventionally, however, in spite of variations in heating temperaturesunder various heat treatments as described, one type of various datawhich are inputted to a proportional operation coefficient, integraltime and derivative time among control parameters are used in PIDcontrol computed by a controller.

Therefore, although there is no particular problem when the wafer isheated to a specific temperature, when the wafer undergoes heattreatment at a temperature different from the specific temperature, adeviation is increased and excess properties are deteriorated since thecontroller cannot cope with the different temperature, therebylengthening recovery time of the heating plate, more specifically, timewhich is required to stabilize the heating plate at a predeterminedtemperature. As a result, there is a risk of causing a reduction in athroughput.

In addition, there is a case where heating temperatures are differentcorresponding to recipes, for example, even in the same PEB, and alsothere is a risk that the recovery time is lengthened.

Similarly also in cooling treatment, various data inputted to controlparameters are fixed to one pattern in PID control computed by aconventional controller. Therefore, although there is no particularproblem when the wafer, which is heated to a specific temperature, iscooled to 23° C., when the wafer, which is heated to a temperaturedifferent from the specific temperature, is placed on a cooling plate,the controller cannot cope with the different temperature, therebylengthening recovery time of the cooling plate and causing a reductionin a throughput.

BRIEF SUMMARY OF THE INVENTION

The present invention is made in view of the aforesaid points and itsobject is to shorten recovery time in heat treatment or coolingtreatment.

In light of the above object, according to a first aspect of the presentinvention, a heat treatment unit of the present invention comprises aheating plate on which a substrate is placed, a heating element capableof heating the heating plate at different temperatures, a temperaturecontroller which control a temperature of the heating element accordingto a transfer function, and a control parameter changing section whichchanges a setting of a control parameter in the transfer function ateach of the different temperatures.

According to a second aspect of the present invention, a heat treatmentunit of the present invention comprises a heating plate on which asubstrate is placed, a heating element capable of heating the singleheating plate at different temperatures, a temperature controller whichcontrols a temperature of the heating element according to a transferfunction represented by the following relational expression (1), and acontrol parameter changing section which changes at least any onesetting of a proportional operation coefficient, integral time orderivative time among control parameters in the transfer function.

u=KP{e+(1/TI)·∫edt+TD·de/dt}  (1)

Therein, “u” expresses an amount of operation, “e” expresses a deviation(a difference between a target temperature and a detected signal (anobserved temperature)), K_(P) expresses the proportional operationcoefficient (a proportional gain), T_(I) expresses the integral time andT_(D) expresses the derivative time, respectively.

According to a third aspect of the present invention, a cooling unitwhich performs cooling treatment on a substrate of the present inventioncomprises a cooling plate on which the substrate is placed, a coolingtemperature adjusting element which adjusts the cooling plate to apredetermined temperature, a temperature controller which controls atemperature of the cooling temperature adjusting element according to atransfer function, a temperature sensor attached to the cooling plate,and a control parameter changing section which changes a setting of acontrol parameter in the transfer function based on a temperature of thecooling plate detected by the temperature sensor after the substratethat is an object to be cooled is placed on the cooling plate.

According to a fourth aspect of the present invention, a cooling unitwhich subjects a substrate to cooling treatment comprises a coolingplate on which the substrate is placed, a cooling temperature adjustingelement which adjusts the cooling plate to a predetermined temperature,a temperature controller which controls a temperature of the coolingtemperature adjusting element according to a transfer functionrepresented by the following relational expression (2), a temperaturesensor attached to the cooling plate, and a control parameter changingunit which changes at least any one setting of a proportional operationcoefficient, integral time or derivative time among control parametersin the transfer function based on a temperature of the cooling platedetected by the temperature sensor after the substrate that is an objectto be cooled is placed on the cooling plate.

u′=KP′{e′+(1/TI′) ·∫e′dt+TD′·de′/dt}  (2)

Therein, “u” expresses an amount of operation, “e′” expresses adeviation (a difference between a target temperature and a detectedsignal (an observed temperature)), K_(p)′ expresses the proportionaloperation coefficient (a proportional gain), T_(I)′ expresses theintegral time and T_(D)′ expresses the derivative time, respectively.

According to a fifth aspect of the present invention, a coolingtreatment method of a substrate of the present invention comprises thestep of changing a setting of a control parameter in a transfer functionbased on a peak temperature when a temperature of a cooling plate israised by the substrate to reach the peak temperature on the occasion ofplacing the substrate on the cooling plate.

According to a sixth aspect of the present invention, a coolingtreatment method of a substrate of the present invention comprises thesteps of placing the substrate on a cooling plate, cooling the substrateto a predetermined temperature by controlling a temperature of thecooling plate according to a transfer function represented by thefollowing relational expression (2), and changing at least any onesetting of a proportional operation coefficient, integral time orderivative time among control parameters in the transfer function basedon a peak temperature when the temperature of the cooling plate israised by the substrate to reach the peak temperature on the occasion ofplacing the substrate on the cooling plate.

u′=KP′{e′+(1/TI′)·∫e′dt+TD′·de′/dt}  (2)

Therein, “u” expresses an amount of operation, “e” expresses a deviation(a difference between a target temperature and a detected signal (anobserved temperature)), K_(P)′ expresses the proportional operationcoefficient (a proportional gain), T_(I)′ expresses the integral timeand T_(D)′ expresses the derivative time, respectively.

According to the heat treatment unit of the present invention, thesettings of the control parameters in the transfer function are changedat every different temperature by the changing unit, whereby thetemperature control means can properly perform the control correspondingto various heating temperatures. Accordingly, it is possible to improveexcess properties and shorten recovery time regardless of thetemperature when the heat treatment is performed on the substrate.Moreover, the stability of the temperature control is increased, wherebythe substrate can be uniformly heated, resulting in the improvement ofthe uniformity of the surface portion thereof. Further, when PIDcontrol, in which even an integral element and a derivative element areadded, is adopted for the temperature controller, a steady-statedeviation (an offset) or thermal vibration is reduced, whereby thetemperature control with higher precision can be performed.

According to the cooling unit of the present invention, the settings ofthe control parameters can be changed based on the temperature of thecooling plate detected by the temperature sensor after the substratethat is an object to be cooled is placed on the cooling plate, wherebythe substrate can be efficiently cooled under the always appropriatecontrol parameters even if its temperature is anything other than anassumed temperature. Therefore, recovery time can be more shortened thanthe conventional one. Additionally, it is possible to perform PIDcontrol by changing at least any one setting of a proportional operationcoefficient, integral time or derivative time among control parametersbased on the temperature of the cooling plate detected by thetemperature sensor after the substrate that is the object to be cooledis placed on the cooling plate, so that the temperature controller, inwhich the settings of the respective control parameters are changed, canoptimally control the temperature of the cooling temperature adjustingelement.

According to the cooling treatment method of the present invention, thefollowing effects can be obtained. For example, when the substrate afterthe heat treatment is placed on the cooling plate, the cooling platereceives an amount of heat from the substrate and its temperature israised. Thereafter, the temperature of the cooling plate is raised toreach a peak temperature. Incidentally, if the relation between the peaktemperature and an initial temperature of the substrate before thecooling treatment is inspected in advance by experiments or the like, itis possible to estimate the initial temperature of the substrate basedon the peak temperature observed by the temperature sensor or the likeprovided on the cooling plate. Accordingly, the temperature of thecooling plate can be optimally controlled regardless of the temperatureof the substrate when it is placed on the cooling plate. As aconsequence, it is possible to improve excess properties and shortenrecovery time regardless of the initial temperature of the substrate.

Additionally, according to the cooling treatment method of the presentinvention, a steady-state deviation (an offset) or the like is reducedand the temperature control with higher precision can be performed byfurther adopting PID control in which even an integral element and aderivative element are added in the transfer function.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription,.or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a plane view of a coating and developing system provided witha baking unit according to embodiments of the present invention and acooling unit according to the same;

FIG. 2 is a front view of the coating and developing system in FIG. 1;

FIG. 3 is a rear view of the coating and developing system in FIG. 1;

FIG. 4 is an internal view of the baking unit according to theembodiments of the present invention;

FIG. 5 is a block diagram showing a control system of the baking unit inFIG. 4;

FIG. 6 is an internal view of the cooling unit according to theembodiments of the present invention;

FIG. 7 is a block diagram showing a control system of the cooling unitin FIG. 6;

FIG. 8 is a graph showing temperature characteristics of a heatingplate;

FIG. 9 is a graph showing an enlarged fragment of graph line indicatingtemperature characteristics of a cooling plate;

FIG. 10 is a graph showing the temperature characteristics of thecooling plate;

FIG. 11 is a table showing recovery time characteristics in anembodiment of heat treatment of the present invention;

FIG. 12 is a graph showing the recovery time characteristics, which ismade up based on the table in FIG. 11;

FIG. 13 is a table showing overshoot characteristics in the embodimentof the heat treatment of the present invention;

FIG. 14 is a graph showing the overshoot characteristics, which is madeup based on the table in FIG. 13;

FIG. 15 is a table showing characteristics of dispersion 3σ of a waferin the embodiment of the heat treatment of the present invention;

FIG. 16 is a graph showing the characteristics of the dispersion 3σ ofthe wafer, which is made up based on the table in FIG. 15;

FIG. 17 is a table showing characteristics of dispersion 3σ of theheating plate in the embodiment of the heat treatment of the presentinvention;

FIG. 18 is a graph showing the characteristics of the dispersion 3σ ofthe heating plate, which is made up based on the table in FIG. 17;

FIG. 19 is a table showing recovery time characteristics in a firstembodiment of cooling treatment in the present invention;

FIG. 20 is a table showing recovery time characteristics in a secondembodiment of cooling treatment in the present invention;

FIG. 21 is a table showing the relation of an initial temperature of thewafer to a peak temperature and reaching time;

FIG. 22 is a graph showing temperature characteristics of a conventionalheating plate; and

FIG. 23 is a graph showing temperature characteristics of a conventionalcooling plate.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention will be described below.

FIG. 1 is a plane view of a coating and developing system 1 in whichbaking units as heat treatment units according to embodiments of thepresent invention and cooling units as cooling treatment units accordingto the same are incorporated, FIG. 2 is a front view of the coating anddeveloping system 1, and FIG. 3 is a rear view of the coating anddeveloping system 1.

As shown in FIG. 1, the coating and developing system 1 has a structurein which a cassette station 2 for carrying, for example, 25 wafersfrom/to the outside to/from the coating and developing system 1 in theunit of cassette and for carrying the wafers W into/from a cassette C, aprocessing station 3 in which various kinds of multi-stage processingunits for performing predetermined processing one by one in the coatingand developing process are disposed, and an interface section 4 forreceiving and delivering the wafer W from/to an aligner (not shown)provided adjacent to the processing station 3, are integrally connected.

In the cassette station 2, a plurality of cassettes C are well mountedat predetermined positions on a cassette mounting table 5 serving as amounting section in a line in an X-direction (a vertical direction inFIG. 1). Further, a wafer carrier 7, which is transferable in thedirection of alignment of the cassettes (the X-direction) and in thedirection of alignment of the wafers W housed in the cassette C (aZ-direction; a vertical direction), is provided to be movable along acarrier guide 8 and is selectively accessible to the respectivecassettes C.

The wafer carrier 7 is structured so as to access also an alignment unit32 and an extension unit 33 which are included in a third processingunit group G3 on the side of the processing station 3 as will bedescribed later.

In the processing station 3, a main carrier unit 13 is provided in thecenter part thereof, and various kinds of processing units are arrangedin a multi-stage on the periphery of the main carrier unit 13 to composeprocessing unit groups. In the coating and developing system 1, thereare four processing unit groups G1, G2, G3 and G4, and the first and thesecond processing unit groups G1, G2 are disposed on the front side ofthe coating and developing system 1, the third processing unit group G3is disposed adjacent to the cassette station 2, and the fourthprocessing unit group G4 is disposed adjacent to the interface section4. Further, as an option, a fifth processing unit group G5 depicted bybroken lines can be additionally arranged on the rear side of thecoating and developing system 1.

In the first processing unit group G1, as shown in FIG. 2, two kinds ofspinner-type solution coating units, for example, a resist coating unit15 for performing resist coating treatment on the wafer W, and adeveloping unit 16 for performing treatment on the wafer W with adeveloping solution supplied are two-tiered in the order from thebottom. Also in the case of the second processing unit group G2, aresist coating unit 17 and a developing unit 18 are similarly two-tieredin the order from the bottom.

In the third processing unit group G3, as shown in FIG. 3, a coolingunit 30 according to the present embodiment, an adhesion unit 31 forincreasing the fixability between a resist solution and the wafer W, thealignment unit 32 for aligning the wafer W, the extension unit 33 forkeeping the wafer W waiting, baking units 34, 35, 36 and 37 according tothe present embodiment and so on are arranged on, for example,eight-stages in the order from the bottom.

In the fourth processing unit group G4, a cooling unit 40, an extensionand cooling unit 41 for spontaneously cooling the placed wafer W, anextension unit 42, a cooling unit 43, baking units 44, 45, 46, 47 and soon are, for example, eight-tiered in the order from the bottom.

In the center part of the interface section 4, provided is a wafercarrier 50. The wafer carrier 50 is structured so as to be accessible tothe extension and cooling unit 41, the extension unit 42 which areincluded in the fourth processing unit group G4, a peripheral aligner51, and the aligner (not shown).

Since any of the baking units 34 to 37, 44 to 47 according to thepresent embodiment has a similar structure, the baking unit 34 will bedescribed as an example. The baking unit 34 is provided with a heatingplate 60 having, for example, a disk shape, on which the wafer W isplaced, a heater 61 capable of heating the single heating plate 60 atdifferent temperatures, a temperature controller 62 which controls thetemperature of the heater 61 according to PID control, and a PID controlparameter changing section 63 which changes settings of PID controlparameters at every different temperature (a target temperature in eachof various heat treatments) as shown in FIG. 4.

To the heating plate 60, attached is a temperature sensor 64. The heater61 is embedded in the heating plate 60 and besides generates heat by anelectric feed from a power source controller 65. The temperature sensor64 is connected to the temperature controller 62 and the power sourcecontroller 65 is connected to the temperature controller 62. Moreover,an amount of operation is calculated by the temperature controller 62based on a detected signal from the temperature sensor 64, the amount ofoperation is transmitted to the power source controller 65 andconsequently controlled so as to make not only the heater 61 but alsothe heating plate 60 generate heat within a range of, for example, 0 to350° C.

Therefore, the single baking unit 34 has a structure in which prebaking(PREBAKE) for performing heat treatment on the wafer W at, for example,200° C. after a resist coating, post-exposure baking (PEB) forperforming heat treatment on the wafer W at, for example, 90° C. afterexposing processing, and postbaking (POSTBAKE) for performing heattreatment on the wafer W at, for example, 300° C. after developingtreatment can be all performed.

FIG. 5 is a block diagram showing a control system of the baking unit34. For example, an input line 66 for inputting a target temperature “r”is firstly connected to the temperature controller 62 as shown in FIG.5. The input line 66 is provided with an addition point 67. The additionpoint 67 is connected to a feedback line 68 for feedbacking the detectedsignal from the temperature sensor 64 (an observed temperature

Further, lines 70, 71 and 72 are branched from a branch point 69connected to the input line 66. The line 70 is provided with aproportional element operator 75, the line 71 is provided with anintegral element operator 76 and the line 72 is provided with aderivative element operator 77, respectively.

Thus, there is a structure inside the temperature controller 62 that adeviation “e” between the target temperature “r” and the observedtemperature “y” is treated by dividing it into three elements of aproportional element, an integral element, and a derivative element sothat each element is computed. Moreover, an operator 78 is connectedthrough a line 80 to an addition point 79 which is the confluence of thelines 70 to 72.

Further, the operator 78 is connected through a line 81 to the powersource controller 65, and the power source controller 65 is connectedthrough a line 82 to the heater 61. By virtue of this, results of therespective computed elements are totaled at the addition point 79, andan amount of operation “u” is calculated by multiplying the totaledresult by a coefficient in the operator 78 and outputted to the powersource controller 65. Finally, an amount of electric power “v” suppliedto the heater 61 is determined in the power source controller 65.

An input line 83 is connected to the PID control parameter changingsection 63. The PID control parameter changing section 63 is connectedto the proportional element operator 75 through a line 84, connected tothe integral element operator 76 through a line 85, connected to thederivative element operator 77 through a line 87, and connected to theoperator 78 through a line 86, respectively.

Integral time T_(I), derivative time T_(D), and a proportional operationcoefficient (a proportional gain) K_(P), which are used for computation,are respectively set in the respective integral element operator 76, thederivative element operator 77 and the operator 78, so that computationis performed by using these respective control parameters.

Incidentally, the respective control parameters can be rewritten in therespective operators 75 to 78. More specifically, data on the respectivecontrol parameters optimum for the target temperature “r” in each ofvarious heat treatments are inspected in advance by experiments or likeand stored in the PID control parameter changing section 63. During theheat treatment, when the target temperature “r” is inputted to the PIDcontrol parameter changing section 63 through the input line 83, the PIDcontrol parameter changing section 63 selects the respective optimumparameters from the stored data based on the target temperature “r” tochange the respective control parameters if necessary.

Besides, in the baking unit 34, provided are three hoisting and loweringpins 90 for hoisting and lowering the wafer W when the wafer W iscarried thereto/therefrom, and the hoisting and lowering pins 90 freelyascend and descend in through holes 91 penetrating the heating plate 60,by a drive mechanism which is not shown. Moreover, on the heating plate60, provided are proximity pins 92 for supporting the wafer W slightlyspaced from the upper surface of the heating plate 60. Therefore, aminute amount of space is formed between the underneath surface of thewafer W and the upper surface of the heating plate 60, therebypreventing the underneath surface of the wafer W from directly cominginto contact with the upper surface of the heating plate 60 so that theunderneath surface of the wafer is not soiled or flawed even if there isdust therebetween.

Next, the cooling unit 30 will be explained as an example since any ofthe cooling units 30, 40 and 43 according to the embodiment of thepresent invention has a similar structure. The cooling unit 30 isprovided with a cooling plate 100 on which the wafer W is placed, aPeltier element 101 for adjusting the cooling plate 100 to apredetermined temperature, a power source controller 102 for supplyingelectric power to the Peltier element 101, temperature controller 103for controlling a temperature of the Peltier element 101 according toPID control by sending an amount of operation to the power sourcecontroller 102, a temperature sensor 104 attached to the cooling plate100, and PID control parameter changing section 105 for changingsettings of PID control parameters based on a temperature of the coolingplate 100 detected by the temperature sensor 104 after the wafer W thatis an object to be cooled is placed on the cooling plate 100, as shownin FIG. 6.

The PID control parameter changing section 105 has a function ofchanging the settings of the control parameters so that the wafer W canbe cooled to, for example, 23° C. as a predetermined temperature.

FIG. 7 is a block diagram showing a control system of the cooling unit30. For example, as shown in FIG. 7, the temperature controller 103 hasa proportional element operator 106, an integral element operator 107, aderivative element operator 108 and an operator 109, and performs thePID control similarly to the temperature controller 62 described above.Integral time T_(I)′, derivative time T_(D)′, and a proportionaloperation coefficient (a proportional gain) K_(P)′ are respectively setin the integral element operator 107, the derivative element operator108, and the operator 109, and computation is performed by using theserespective control parameters. Further, the PID control parameterchanging section 105 and the temperature sensor 104 are connectedthrough a line 110 so that a detected signal from the temperature sensor104 (an observed temperature “y′”) is transmitted to the PID controlparameter changing section 105. It should be noted that the samereference numerals and symbols will be used for components having thesubstantially same functions and structures to omit the repeateddescription in FIG. 5 and FIG. 7.

Besides, in the cooling unit 30, provided is a flow path 111 fordissipating heat of the Peltier element 101. The flow path 111 runsinside the cooling plate 100 so that cooling water, which is suppliedfrom a cooling water supply mechanism which is not shown, flows therein.In addition, the three hoisting and lowering pins 90 freely ascend anddescend in the through holes 91 and the proximity pins 92 are providedon the cooling plate 100 in the same manner as that in the baking unit34 described above.

Next, functions of the above-structured baking unit 34 and the coolingunit 30 after the heat treatment in the baking unit 34 will be explainedbased on an example of coating and developing treatment of the wafer Wperformed in the coating and developing system 1.

First, the wafer carrier 7 takes an unprocessed wafer W out of thecassette C to carry it into the alignment unit 32 included in the thirdprocessing unit group G3. Second, the wafer, of which alignment iscompleted in the alignment unit 32, is sequentially transferred to theadhesion unit 31, the cooling unit 30, and the resist coating unit 15 or17 by the main carrier unit 13 to undergo predetermined processings.After that, the wafer W is transferred to the baking unit 34 and aresidual solvent in the resist is vaporized.

The heat treatment of the wafer W will be now described. First, thetemperature control of the heating plate 60 by the temperaturecontroller 62 will be explained. The target temperature “r” of theheating plate 60 is inputted through the input line 66 as shown in FIG.5. Moreover, the target temperature “r” is also inputted to the PIDcontrol parameter changing section 63 and the PID control parameterchanging section 63 sets the respective control parameters of therespective operators 75 to 78 based on the target temperature “r”.

Meanwhile, a temperature of the heating plate 60 is detected from thetemperature sensor 64 and the detected signal (the observed temperature“y”) is transmitted through the feedback line 68 to the addition point67. At the addition point 67, a subtraction is performed between thetarget temperature “r” and the detected signal (the observed temperature“y”) and a difference between the target temperature “r” and thedetected signal (the observed temperature “y”) is calculated as thedeviation “e”. The deviation “e” obtained in this manner is divided intothree components of a proportional component “p”, an integral component“i”, and a derivative component “d” and the three components aretransmitted to the respective operators 75 to 77 through the respectivelines 70 to 72.

The computation is performed in the respective operators 75 to 77 byusing the respective control parameters such as the integral time T_(I),and the derivative time T_(D), and transmitted to the addition point 79.The results of the computation in the above-described respectiveoperators 75 to 77 are totaled at the addition point 79, and furthermultiplied by the proportional operation coefficient K_(P) in theoperator 78 so that the amount of operation “u”, which is represented bya formula (3) described below, is calculated.

u=KP{e+(1/TI)·∫edτ+TD·de/dt}  (3)

Therein, “∫edτ” indicates the integral component of the deviation “e”and “de/dt” indicates the derivative component of the deviation “e”.

The following is a formula (4) when the amount of operation “u” isconsidered as a function of time and represented as a function u(t) oftime.

u(t)=KP·{e(t)+(1/TI)·∫e(τ)dτ+TD·de(t)/dt}  (4)

Therein, “e(t)” indicates a deviation in time “t”, “∫e(τ)dτ” indicatesthe integral component of the deviation “e” and “de(t)/dt” indicates thederivative component of the deviation e(t) in the time “t”.

An amount of operation u(t) thus obtained is transmitted through theline 81 to the power source controller 65. The power source controller65 supplies an amount of electric power v(t) through the line 82 to theheater 61 based on the amount of operation u(t), and the heater 61supplies an amount of heat corresponding thereto to the heating plate 60based on the amount of electric power v(t).

In this manner, amounts of operation u(t₀), u(t₁), u(t₂), u(t₃) (to becontinued) are transmitted to the power source controller 65 inaccordance with the lapse of time such as t₀, t₁, t₂, t₃, (to becontinued) and the power source controller 65 makes the heater 61generate heat based on the amounts of operation to heat the heatingplate 60. The temperature is detected by the temperature sensor 64 andfeedback control is continuously performed based on the deviation “e”which is the difference between the target temperature “r”, so that thetemperature of the heating plate 60 becomes the target temperature “r”.

Next, the heat treatment by the heating plate 60 is explained based onFIG. 8. In FIG. 8, a horizontal axis indicates heating time [s,(second)] and a vertical axis indicates the temperature of the heatingplate 60 [°]. First, the target temperature “r” is inputted to thetemperature controller 62 and heating by the heater 61 is performedbefore the wafer W is placed so that the heating plate 60 is maintainedat the target temperature as shown by Graph Line “m” in FIG. 8 (time t₀to t₁).

Subsequently, the wafer W having a temperature of 23° C. (a roomtemperature) is placed on the heating plate 60. Although the heatingplate 60 loses an amount of heat to the wafer w and its temperature islowered (time t₁ to t₂), the temperature of the heater 61 can beproperly controlled in the temperature controller 62 in which therespective optimum parameters are set, thereby keeping a drop intemperature of the heating plate 60 to a minimum. Thereafter, thetemperature control of the heater 61 is performed as well, and thetemperature of the heating plate 60 is raised in such a manner thatsubstantial overheating does not occur (time t₂ to t₃). After that, whenthe temperature of the heating plate 60 is slightly over the targettemperature “r”, it is made reach the target temperature “r” orthereabout by weakening heating operation of the heater 61 (time t₃ tot₄). In this manner, the temperature of the heating plate 60 isstabilized at the target temperature “r”.

Then, the wafer W, which is in a state of a high temperature by the heattreatment, is transferred to the cooling unit 30 and cooled to 23° C.Now cooling treatment of the wafer W is described. First, thetemperature control of the cooling plate 100 by the temperaturecontroller 103 is performed following almost the same procedure used bythe temperature controller 62, and an amount of operation “u′”, which isrepresented by a formula (5) described below, is calculated.

u′=KP′{e′+(1/TI′)·∫e′dτ+TD′·de′/dt}  (5)

Therein, “∫e′dτ” indicates an integral component of a deviation “e” and“de/dt” indicates a derivative component of the deviation “e′” in time“t”.

The following is a formula (6) when the amount of operation “u′” isconsidered as a function of time and represented as a function u′(t) oftime.

 u′(t)=KP′{e′(t)+(1/TI′)·∫e(τ)dτ+TD′·de(t)/dt}  (6)

Therein, “e′(t)” indicates a deviation in the time “t”, “∫e′(τ)dτ”indicates an integral component of the deviation “e′”, and “de′(t)/dt”indicates a derivative component of the deviation e′(t) in the time “t”.

The amount of operation u′(t) thus obtained is transmitted through theline 81 to the power source controller 102 and the power sourcecontroller 102 supplies an amount of electric power v′(t) through theline 82 to the Peltier element 101 based on the amount of operationu′(t). Then the Peltier element 101 cools the cooling plate 100.

A detected signal from the temperature sensor 104 (an observedtemperature “y′”) is inputted to the PID control parameter changingsection 105, and the PID control parameter changing section 105 sets therespective control parameters of the respective operators 106 to 109based on the detected signal (the observed temperature “y′”).

The settings are changed by the PID control parameter changing section105 in the following. For example, the cooling plate is initiallymaintained at 23° C. (the room temperature) as shown by Graph “n” inFIG. 9 (time to to t₁). When the wafer W subjected to heat treatment issubsequently placed on the cooling plate 100, the cooling plate 100receives an amount of heat from the wafer W and its temperature israised to reach a peak temperature T_(P) (time t₁ to t₂). Incidentally,the relation of an initial temperature of the wafer before the coolingtreatment to the peak temperature T_(P) is inspected in advance byexperiments or the like, and the relation is tabulated and stored in amemory (not shown) of the PID control parameter changing section 105beforehand. Consequently, the initial temperature of the wafer can beestimated by detecting the peak temperature T_(p) after the wafer W isplaced. Further, the PID control parameter changing section 105 sets therespective optimum control parameters, which are inspected in advance byexperiments or the like as well, in the respective operators 106 to 109based on the estimated temperature of the wafer.

Next, the cooling treatment by the cooling plate 100 is explained basedon FIG. 10. In FIG. 10, a horizontal axis indicates cooling time [sec.]and a vertical axis indicates the temperature of the cooling plate 100[° C.]. The wafer W is placed on the cooling plate 100 as shown by GraphLine “n” in FIG. 10. The settings of the PID control parameters arechanged based on the peak temperature T_(p) when the temperature of thecooling plate 100 is raised by the wafer W to reach the peak temperatureT_(P) on the occasion of placing the wafer W on the cooling plate 100.In the temperature controller 103 in which the respective optimumcontrol parameters are set, the temperature of the Peltier element 101can be properly controlled, whereby the temperature of the cooling plate100 can be lowered in such a way that substantial overcooling does notoccur (time t₂ to t₃). Then, when reaching a bottom temperature T_(B),the temperature of the cooling plate 100 is raised by weakening coolingoperation by the Peltier element 101 (time t₃ to t₄). Thus, thetemperature of the cooling plate 100 is stabilized at 23° C.

Subsequently, the wafer W in a state of the room temperature by thecooling treatment is sequentially transferred to the extension unit 33,the peripheral aligner 51, the aligner (not shown), the baking unit 34,the cooling unit 30, the developing unit 16 or 18, the baking unit 34,and the cooling unit 30 to undergo predetermined processings.

In the baking unit 34, each individual target temperature “r” isinputted to the temperature controller 62 during heat treatment aftereither the exposing processing or the developing treatment, so that thetemperature of the heating plate 60 is stabilized at the targettemperature “r” in short recovery time in the same manner as that duringthe heat treatment after the resist coating. Additionally, in thecooling unit 30, each peak temperature T_(P) is read during coolingtreatment after either the post-exposure baking or the postbaking, sothat the temperature of the cooling plate 100 is stabilized at 23° C. inshort recovery time in the same manner as that during the coolingtreatment after the prebaking.

According to such baking unit 34, the settings of the respective PIDcontrol parameters are changed by the PID control parameter changingsection 63 at every different temperature, thereby enabling thetemperature controller 62 to properly perform the temperature controlcorresponding to the various heating temperatures. Accordingly, it ispossible to improve excess properties and shorten the recovery timeregardless of the temperature when the heat treatment is performed onthe wafer W. Therefore, a throughput is increased. Moreover, thestability of the temperature control is increased, whereby the wafer wcan be uniformly heated, resulting in the improvement of the uniformityof the surface portion thereof.

On the other hand, according to the cooling unit 30, the settings of therespective PID control parameters can be changed based on the peaktemperature T_(P) after the wafer w that is the object to be cooled isplaced on the cooling plate 100, whereby the temperature controller 103can optimally control not only the temperature of the Peltier element101 but also the temperature of the cooling plate 100 regardless of thetemperature of the wafer when it is placed on the cooling plate 100.Additionally, even if the temperature of the wafer W that is the objectto be cooled is anything other than an assumed temperature, the wafer Wcan be efficiently cooled under the always appropriate controlparameters. Therefore, it is possible to improve the excess propertiesand shorten the recovery time regardless of the initial temperature ofthe wafer. As a result, the throughput is increased.

Further, the PID control, in which even the integral element and thederivative element are added, is adopted for the temperature controller62 and 103, whereby a steady-state deviation (an offset) or thermalvibration is reduced and the temperature control with higher precisioncan be performed.

Incidentally, a route of carrying the wafer W in the coating anddeveloping system 1 can be freely set so that the various heattreatments can be performed in the baking units 35 to 37 and 44 to 47,and the various cooling treatments can be performed in the cooling units40 and 43. Moreover, a substrate may be the rectangular substrate suchas an LCD substrate as well as the disk-shaped substrate such as theabove-described wafer W.

Next, results, which are obtained by inspecting the respective controlparameters and the characteristics such as the recovery time and theuniformity of the surface portion when the heat treatment is performedon the wafer W using the baking unit 34 according to the embodiment ofthe present invention, will be described.

In the baking unit 34, the heat treatment is performed by setting therespective control parameters in such a manner that K_(P)=2.8, T_(I)=80,T_(D)=15 in a pattern 1, by setting the respective control parameters insuch a manner that K_(P)=2.8, T_(I)=80, T_(D)=7 in a pattern 2, and bysetting the respective control parameters in such a manner thatK_(P)=4.0, T_(I)=49, T_(D)=12 in a pattern 3. In these patterns 1 to 3,it is determined how the characteristics of the recovery time, anovershoot, the uniformity of the surface portion of the heating plate60, and the uniformity of the surface portion of the wafer w are changedrespectively when the temperature of the heating plate 60 issequentially changed to such as 90° C., 120° C., 150° C., and 180° C.The results are shown in FIGS. 11 to 18.

FIG. 11 is a table and FIG. 12 is a graph respectively showing therecovery time characteristics, FIG. 13 is a table and FIG. 14 is a graphrespectively showing the overshoot characteristics, FIG. 15 is a tableand FIG. 16 is a graph respectively showing the characteristics of theuniformity of the surface portion of the wafer W, FIG. 17 is a table andFIG. 18 is a graph respectively showing the characteristics of theuniformity of the surface portion of the heating plate 60. Graph Line a1in FIG. 12, Graph Line a2 in FIG. 14, Graph Line a3 in FIG. 16, GraphLine a4 in FIG. 18 shows the respective characteristics in the pattern1. Graph Line b1 in FIG. 12, Graph Line b2 in FIG. 14, Graph Line b3 inFIG. 16, Graph Line b4 in FIG. 18 shows the respective characteristicsin the pattern 2. Graph Line c1 in FIG. 12, Graph Line c2 in FIG. 14,Graph Line c3 in FIG. 16, Graph Line c4 in FIG. 18 shows the respectivecharacteristics in the pattern 3.

In such baking unit 34, the patterns 1 to 3 are stored in the PIDcontrol parameter changing section 63 beforehand. In addition, the PIDcontrol parameter changing section 63 sets the respective controlparameters of the temperature controller 62 according to, for example,the pattern 1 when the target temperature “r” is 120° C. and accordingto the pattern 2 when the target temperature “r” is 180° C. As a result,when the target temperature “r” is 120° C., it is possible to reduce therecovery time to 30 seconds, the overshoot to 0.2° C., dispersion 3σ inthe temperatures of the wafer surface portion (three times a standarddeviation ) to 0.85° C., and dispersion 3σ in the temperatures of theheating plate 60 (three times a standard deviation σ) to 0.26° C.,respectively, and when the target temperature “r” is 180° C., it ispossible to reduce the recovery time to 44 seconds, the overshoot to0.5° C., dispersion 3σ in the temperatures of the wafer surface portion(three times a standard deviation σ) to 1.63° C., and dispersion 3σ inthe temperatures of the heating plate 60 (three times a standarddeviation (σ) to 0.77° C., respectively. If the respective controlparameters of the temperature controller 62 are fixed to those in thepattern 1, the recovery time becomes 61 seconds when the targettemperature “r” is 180° C. Thus, it is possible to recognize that therecovery time and the characteristics such as the uniformity of thesurface portion of the wafer W are made preferable by changing therespective control parameters depending on the target temperature “r”.

Next, the recovery time characteristics are inspected by performing thecooling treatment on the wafer W using the cooling unit 30 according tothe embodiments of the present invention.

As a first embodiment of the cooling treatment, the recovery time ismeasured when the initial temperature of the wafer is in a lowtemperature range (90° C., 120° C.). Incidentally, conditions are set asfollows. An ambient temperature is set at 23° C., an amount of coolingwater is set at 3 liters per minute, a proximity gap is set at 0.10 mm,carrying time required to carry the wafer from the baking unit 34 to thecooling unit 30 is set at 6 seconds, and the respective controlparameters are set in such a manner that K_(P)=2, A=0.8, T_(I)=5,T_(D)=1, and then two cases where a temperature of the cooling water is90° C. and 120° C. are inspected. The results are shown in FIG. 19.Incidentally, “A” is a constant for preventing an overshoot in advanceby limiting a range in which integral operation is made effective, andits unit is [° C.].

As shown in FIG. 19, the recovery time can be shortened to 30 seconds orless when the initial temperature of the wafer is in the low temperaturerange (90° C., 120° C.) by selecting the respective control parametersdescribed above.

Further, as a second embodiment of the cooling treatment, the settingsof the respective control parameters are changed to K_(P)=2, A=1,T_(I)=5, T_(D)=2, and the recovery time when the initial temperature ofthe wafer is 90° C., 120° C., 150° C., and 200° C. is measured. Theresults are shown in FIG. 20.

The recovery time can be shortened by selecting the respective controlparameters as shown in FIG. 20. For example, it is preferable that thetemperature control is performed according to the settings of therespective control parameters in the first embodiment when the initialtemperature of the wafer is 90° C. or 120° C., and the temperaturecontrol is performed according to the settings of the respective controlparameters in the second embodiment when the initial temperature of thewafer is 150° C. or 200° C. Consequently, the recovery time can beshortened depending on the initial temperature of the wafer.

Furthermore, the peak temperature T_(P) and reaching time required toreach the peak temperature T_(P) (corresponding to time t₁ to t₂ inabove FIG. 10) when the initial temperature of the wafer is 200° C. or250° C. are measured. The results are shown in FIG. 21.

The relation between the peak temperature T_(p) and the initialtemperature of the wafer is tabulated and stored in the PID controlparameter changing section 105 beforehand as shown in FIG. 21. Therespective optimum control parameters can be selected according to theinitial temperature of the wafer estimated from the peak temperatureT_(P), when the cooling treatment is performed. The relation between theinitial temperature of the wafer and the reaching time may naturally bestored.

According to the present invention, it is possible to improve the excessproperties and shorten the recovery time regardless of the temperaturewhen the heat treatment is performed on the substrate. As a result, thethroughput can be increased. Moreover, the stability of the temperaturecontrol is increased, whereby it is possible to heat the substrateuniformly to improve the uniformity of the surface portion thereof. Thesteady-state deviation (the offset) or thermal vibration is reduced,whereby the temperature control with higher precision can be performed.

According to the present invention, it is possible to improve the excessproperties and shorten the recovery time required for cooling to thepredetermined temperature regardless of the temperature of the substratewhen it is placed on the cooling plate. Accordingly, the throughput canbe increased. Additionally, the steady-state deviation (the offset) orthe like is reduced, whereby the temperature control with higherprecision can be performed.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A heat treatment unit for subjecting a substrateto heat treatment comprising: a heating plate on which the substrate isplaced; a heating element which heats said heating plate at differenttemperatures; a temperature controller which controls a temperature ofsaid heating element according to a transfer function; and a controlparameter changing section which changes a setting of a controlparameter in the transfer function at each of the differenttemperatures.
 2. The heat treatment unit according to claim 1, whereinsaid temperature controller controls the temperature of said heatingelement according to PID control.
 3. The heat treatment unit accordingto claim 1, wherein said control parameter changing section includes aPID control parameter changing section which changes settings of PIDcontrol parameters at every different temperature.
 4. The heat treatmentunit according to claim 1, wherein said heating plate includes atemperature sensor attached thereto, and said temperature controllercalculates an amount of operation based on a detected signal from saidtemperature sensor and the parameters of said control parameter changingsection, and controls said heating element in accordance with the amountof operation so that said heating plate generates heat within a givenrange.
 5. The heat treatment unit according to claim 4, wherein saidcontrol parameter changing section stores data on a plurality of controlparameters optimum for a target temperature in each of various heattreatments which are inspected in advance, and selects the optimumparameters from the stored data based on the target temperature tochange the control parameters.
 6. The heat treatment unit according toclaim 4, wherein said heating element is embedded in said heating plate.7. A heat treatment unit for subjecting a substrate to heat treatmentcomprising: a heating plate on which the substrate is placed; a heatingelement which heats said heating plate at different temperatures; atemperature controller which controls a temperature of said heatingelement according to a transfer function represented by the followingrelational expression; and a control parameter changing section whichchanges at least any one setting of a proportional operationcoefficient, integral time or derivative time among control parametersin the transfer function at each of the different temperatures, u=KP{e+(1/TI)·∫edt+TD·de/dt} where “u” expresses an amount ofoperation, “e” expresses a deviation, K_(P) expresses the proportionaloperation coefficient (a proportional gain), T_(I) expresses theintegral time and T_(D) expresses the derivative time, respectively.